System and method of enhancing WiFi real-time communications

ABSTRACT

Systems and methods of enhanced real-time communications between WiFi devices. In one embodiment of the present invention a method for enhanced payload protection in a WiFi system includes transmitting multiple copies of data packets in successive frame body transmissions. In another embodiment, a method for enhanced communications over a WiFi link includes examining a unit ID packet to determine a destination of a data payload when errors are detected in IP and/or MAC headers. If a destination is determined, the packet is corrected and forwarded to the device based on the unit ID determination. In another embodiment, a method for enhanced real-time communications in a WiFi network includes establishing a communications frame that includes an active timeslot, preferably based on U-APSD, for a WiFi device to use for transmission of successive audio data packets transmitted between the WiFi handset and AP.

BACKGROUND

1. Field of the Invention

This application claims the benefit of U.S. Provisional Application No.60/754,604 filed Dec. 30, 2005, which is herein incorporated byreference in its entirety.

The present invention relates generally to wireless communicationssystems. More particularly, the present invention relates to systems forimproved communications in wireless devices using WiFi communicationslinks.

2. Background

Wireless communications technology affords users great flexibility incommunications, including audio communications, email, video, and otherdata transfer.

While cellular networks are deployed widely for convenient voicecommunications, use of data-intensive wireless communications hasincreased dramatically in recent years, in part due to the deployment oftechnology (such as WiFi) based on the 802.11 family of standards. Thelatter technology is particularly suited for users of data terminalssuch as portable computers who enjoy “portable” access to data networksthrough access points (APs), whether at home, in an office, hotel,school, or coffee shop.

Because 802.11 (the term “WiFi” is used interchangeably with “802.11”herein to indicate a wireless communications based on an 802.11standard) technology has been developed to facilitate datacommunications, such as email, web access, and the like, a focus hasbeen on assuring data transmission, while less attention has been paidto applications that involve real-time communications, such as audio andvideo transmission. Accordingly, 802.11-based devices have not beenwidely deployed as audio or video devices.

A first problem associated with the use of 802.11 for real-timeapplications is the use of a frame check sequence (FCS) included in apayload packet for determining whether to send an acknowledgment (ACK)for a particular transmitted payload packet. However, in real-time voiceand streaming video applications, it is not possible to use an ACKmechanism.

Because every data packet is subject to an ACK mechanism intransmissions using the 802.11 standard, a large overhead is added todata transmissions. While desirable to ensure the reliability of datatransmissions, this creates an often unnecessary transmission bottleneckfor real-time applications. For example, in wireless transmission ofdata from a WiFi terminal to an access point (AP), if a single error isdetected in the Media Access Control (MAC) header or payload of an802.11 packet transmission, the packet is rejected. Rejection based onsingle errors may desirable in the case of data transmitted usinginternet protocol (IP), where the single error could be located in an IPaddress field, and could cause the packet to be improperly directed tothe wrong IP address by the AP.

However, single errors located in voice packets, for example, are ofteneasily correctible or have negligible influence on the integrity of thecommunications. Thus, voice message transmission using WiFi technologyoften entails frequent retries initiated because of error detection, orloss of audio, resulting in inferior audio quality.

Additionally, 802.11 wireless terminals are susceptible to interferencefrom other nearby RF devices. Because transmission occurs at a fixedfrequency, frequency diversity cannot be deployed to avoid RFinterference with another device operating at about the same frequency.Although a sequence of retries of transmission of an audio packet can beattempted to avoid interference using time diversity, the retries canhave adverse consequences. For example, when two handset devicesoperating in close proximity each employ a series of retries to avoidexternal interference, the total frame time may exceed 10 ms and lead tounstable communications.

Accordingly, it will be recognized that a need exists to improve 802.11communications for real-time applications.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a method for enhancedpayload protection in a WiFi system includes receiving a first datapacket in a buffer. The first data packet and a second data packet aretransmitted in a first frame body between a WiFi terminal and accesspoint (AP). The first data packet and a third data packet aretransmitted in a second frame body between the WiFi terminal and AP. Byrepeating the above steps for other data packets in the above manner,two copies of each data packet can be sent between the WiFi terminal andAP. The two copies are received in a buffer. A determination is made asto a best copy of the two copies and the best copy of the two copies isforwarded to a receiver.

In another embodiment of the present invention, a method for enhancedpayload protection in a WiFi system includes a step of storing a datapacket in a buffer. An FEC packet based on the data packet is alsostored in the buffer. The Data packet and FEC packet are transmittedbetween a WiFi terminal and an AP. The FEC packet is applied to the datapacket to produce a corrected data packet. The corrected data packet isforwarded to a receiver.

In another embodiment of the present invention, a method for enhancedcommunications over a WiFi link includes transmitting a data payloadover a first payload. An error is detected using an FCS packet. The datapayload is sent to a packet correction layer. The packet correctionlayer determines the nature of the error. In one embodiment of thepresent invention, if it is determined that an error exists in the IPand MAC fields, the packet correction layer examines a unit ID packet todetermine a destination of the data payload. If a destination isdetermined, the packet is corrected and forwarded to the device based onthe unit ID determination.

In another embodiment of the present invention, a method for enhancedcommunications in a WiFi network includes a step of establishing a framecharacterized by a frame interval for transmission of successive audiodata packets transmitted between a WiFi handset and AP. A registrationfrom the WiFi handset is received. An active timeslot for transmissionof audio data packets between the WiFi handset and AP is arranged withinthe frame. A trigger from the WiFi handset is received. Data isdelivered to the handset and received from the handset, wherein theactive timeslot is configured to avoid overlap with active timeslotsarranged for other WiFi devices in active communication with the AP.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one exemplary data payload (frame body) structurethat is used in transmission of successive 802.11 payload packets,according to an embodiment of the present invention.

FIG. 2 illustrates a three-data packet frame body structure, accordingto another embodiment of the present invention.

FIG. 3 illustrates an exemplary frame body arranged according to anotherembodiment of the present invention.

FIG. 4 illustrates a reference IP packet that can be used to transmitvoice or other data from a transmitter using 802.11 protocol, where thedata is to be sent over an IP network.

FIG. 5 illustrates exemplary steps in a method for improving an 802.11link according to one embodiment of the present invention.

FIG. 6 illustrates an exemplary 802.11 data packet payload, according toone embodiment of the present invention.

FIG. 7 illustrates an exemplary frame structure for enhanced WiFicommunications, according to one embodiment of the present invention.

FIG. 7A illustrates an exemplary frame structure, in accordance withanother embodiment of the present invention.

FIG. 7B illustrates an exemplary frame structure arranged in accordancewith another embodiment of the present invention.

FIG. 7C illustrates a frame structure that adds two handset active slotsto that depicted in FIG. 7B.

FIG. 7D illustrates a frame structure that corresponds to a scenario inwhich an extra handset active slot is added to two previously activehandset slots in the case where the data transmission rate is alsodrastically reduced.

FIG. 7E illustrates a frame structure that adds a fourth handset activeslot in the case of a lower data transmission rate, as illustrated inFIG. 7D.

FIG. 8 depicts a WiFi system arranged in accordance with one embodimentof the present invention.

FIG. 9 illustrates one implementation of U-APSD.

FIG. 10 illustrates exemplary steps in a method for enhancedcommunications in a WiFi system, according to another embodiment of thepresent invention.

FIG. 11 illustrates exemplary steps in a method for enhancedcommunications in a WiFi system, according to another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Before one or more embodiments of the invention are described in detail,one skilled in the art will appreciate that the invention is not limitedin its application to the details of construction, the arrangements ofcomponents, and the arrangement of steps set forth in the followingdetailed description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or being carried outin various ways. Also, it is to be understood that the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting.

In an 802.11 payload packet used to transmit standard data a frame checksequence (FCS) packet is inserted together with a frame body (payload)in the payload packet. The FCS is used in conjunction with anacknowledgment mechanism to determine whether to send the payloadpacket. In standards such as 802.11e that are geared toward real-timedata transmission, no acknowledgement mechanism is supported.Accordingly, real-time voice or streaming video may be sent without anyFCS. The quality of such transmissions can therefore be less than ideal.

FIG. 1 illustrates one exemplary data payload (frame body) structure 100that is used in transmission of successive 802.11 payload packets,according to an embodiment of the present invention. At time T1, framebody structure 100 is included in 802.11 payload packet 102, which caninclude header and other address fields (not shown). Payload packet 102can be transmitted from a WiFi handset to a wireless AP, for example. Inone embodiment of the present invention, frame body structure 100 is adual voice packet structure that includes voice packet slot 104 andvoice packet slot 105. As depicted, voice packet slots 104 and 105contain consecutive voice packets received in a buffer. At time T1, forexample, voice packets N and N−1 are included in frame body 100 of802.11 payload packet 102. After payload packet 102 is received at thewireless AP, voice packets N and N−1 can be stored locally in the AP. Attime T2, voice frame body structure 100 of payload packet 112 includesvoice packets N and N+1. Voice packet N+1 can be a voice packettransmitted consecutively after voice packet N to a buffer. Both voicepackets N and N+1 can then be transmitted at time T2 to the wireless APin payload packet 112. Likewise, at time T3, voice packets N+1 and N+2are transmitted in frame body 100 of 802.11 payload packet 122.Accordingly, each voice packet can be transmitted twice to the wirelessAP in successive 802.11 payload packets. By separating in time thetransmission of nominally identical voice packets, dual packet framebody structure 100 provides a mechanism to increase the probability thatat least one of the two nominally identical voice data packets is sentwithout error, especially in the presence of interference where errorgeneration in any given packet can occur. Accordingly, the receivingdevice, such as an AP, can then determine which of the two copies of agiven voice packet to transmit to a receiver for playing.

FIG. 2 illustrates a three data packet frame body structure 200according to another embodiment of the present invention. In this case,the operation of frame body structure 200 is illustrated by inclusion ofredundant data packets in a series transmitted 802.11 payload packetsusing payload slots 203, 204, 205. Within each 802.11 payload packet,frame body structure 200 includes three different data packets, forexample, voice data packets. The operation of frame body structure 200is analogous to that of frame body structure 100, except that instead ofsending each voice data packet twice, each voice data packet is sentthrice. Thus, for example, voice data packet N is sent consecutively attimes T1, T2 and T3 in 802.11 payload packets 205, 204, and 203,respectively. The three copies of each voice payload packet can bestored in a buffer of a receiving device, and the best copy can beaccepted for transmission to a receiver.

In other embodiments of the present invention, the data packets can bevideo or other types of data.

FIG. 3 illustrates an exemplary frame body 300 arranged according toanother embodiment of the present invention. Frame body 300 includesdata packet 302 and forward error correction (FEC) packet 304. Datapacket 302 can be, for example, a voice packet or video packet. When adevice (not shown) transmits data packet 302 as part of an 802.11payload packet (not shown), the transmitter can calculate FEC bits basedon data packet 302 and a given algorithm, and append the FEC bits aspacket 304 to the data.

A receiver of 802.11 payload packet can then use the algorithm and thereceived FEC packet 304 to perform error corrections, if necessary, onthe data packet 302.

FIG. 4 illustrates a reference IP packet 400 that can be used totransmit voice or other data from a transmitter using an 802.11protocol, where the data is to be sent over an IP network. IP packet 400includes physical layer header 402, MAC header 404, FCS 406, as well asIP header 408, CRC 410, UDP header 412, RTP header 414, and data payload416. In a conventional implementation, when a transmitting device sendsvoice data, for example, an 802.11 WiFi handset used to transmit voicein a voice-over-internet-protocol (VOIP) call, the voice data ispackaged as payload 416 within packet 400 and sent over a wireless linkto a receiver, such as an AP. When the packet is received, the AP checkspacket 400, and if no errors are found, forwards the packet fortransmission over an IP data network. As described below, errors aredetected in conventional 802.11 transmission using FCS. FCS generallyinvolves extra checksum characters that are added in a frame for errordetection and correction. The sending device computes a checksum on theentire frame and sends this along. The receiving device computes thechecksum on the received frame using the same algorithm, and compares itto the received FCS. In this manner, the receiver can detect whether anydata was lost or altered in transit. In conventional implementation, anyerror detected in packet 400 by a receiving AP will cause the entirepacket to be rejected.

The 802.11 MAC header 404 generally comprises a destination address forthe packet, as well as a source address, which is the unique address ofthe sending device. In addition, IP header 408 contains the terminaldevice IP address. Accordingly, any errors in the IP or MAC headerscould cause failure of delivery of packet 400 to the right address.Thus, in conventional 802.11 protocol, rejection of packet 400 precludesdelivery of packets to the wrong address.

However, the single bit error rejection comes at a cost. The location ofa bit error is not determined in the FCS process. Accordingly, arejected IP packet, such as packet 400, could contain an error in anyfield, for example, voice payload 416, or MAC header 404. In the latterfield, rejection of the packet prevents possible improper packetdelivery. But a single error in voice payload 416 is unlikely to causedelivery problems, and may present no significant degradation in thequality of voice data contained therein.

Yet, the entire packet 400 is rejected, leading to the need to resendthe voice data, and possible degradation of audio quality during a VOIPcall.

FIG. 5 illustrates exemplary steps in a method for improving an 802.11link according to one embodiment of the present invention. In step 501,an 802.11 IP packet is received over an air interface at a receivingdevice, such as an AP. The IP packet contains a data packet payload, forexample, a voice data packet.

In step 502, an error is detected in an 802.11 IP packet. For example,an AP using an FCS field in the received packet detects that the 802.11IP packet as received contains errors.

In optional step 504, the receiving unit determines whether to forwardthe 802.11 IP packet for further evaluation. In one embodiment of thepresent invention, the process moves directly from step 502 to step 510below. In other words, the receiving unit, for example, an AP,automatically determines to forward all packets received with errors forfurther evaluation. In another embodiment of the present invention,screening of the incoming 802.11 IP packet is performed by the receivingdevice. For example, based on MAC filtering or a similar procedure, anAP can determine whether the 802.11 IP packet was received from a known(registered) WiFi handset. The AP may be preconfigured to only processerrors in packets received from registered devices. Accordingly, if thehandset not registered, the process moves to step 506.

In step 506, the received IP packet containing errors is rejected.

In step 508, the receiver waits to receive another 802.11 IP packet. Forexample, the sending device can resend a copy of the voice data packetcontained in the first 802.11 IP packet. The process can then return tostep 501.

If, in step 504, the handset is registered, then the process moves tostep 510.

In step 510, the 802.11 IP packet with errors is forwarded to a packetevaluation layer. The packet evaluation layer (PEL) can be software thatis executed by a processor in the AP.

In step 512, the PEL operates to determine the location and nature ofthe error or errors in the received 802.11 IP packet. For example, thePEL may determine that the error is a non-address error. The term“non-address error” denotes an error in the 802.11 packet locatedoutside of the IP or MAC headers. If the error is a non-address error,the process moves to step 514 where error corrections to non-addresserrors are performed before delivery of the payload.

In step 512, if an “address error” is detected, that is, one occurringin the IP or MAC headers, the process moves to step 516.

In step 516, the receiver (AP) determines if any address information isrecoverable from the MAC and/or IP headers, such that the 802.11 packetcan be transmitted properly. If so, then the process moves to step 518where the 802.11 packet is forwarded for delivery to the IP network.

In step 516, if the receiver determines that errors in the MAC and IPheader information preclude proper delivery of the 802.11 packet, theprocess moves to step 520.

In step 520, the data packet payload is evaluated to recover addressinformation. In a preferred embodiment of the present invention, thedata packet payload contains a data packet, and FEC packet, and a UNITID packet. The data packet can be a voice packet or video packet, forexample. FIG. 6 illustrates an exemplary 802.11 data packet payload 600,according to one embodiment of the present invention. Payload 600contains voice payload 602, FEC packet 604 and UNIT ID packet 606. FECpacket 604 performs forward error correction on UNIT ID packet 606 toensure that bits contained in the UNIT ID are unlikely to suffer atransmission error. UNIT ID preferably contains information thatuniquely identifies the 802.11 receiving device that is to receive the802.11 IP packet. Thus, in step 520, the UNIT ID packet can be used todetermine the destination of the 802.11 IP packet even if the IP and MACheaders have been corrupted.

After determining the correct address, the process moves to step 518,where the data packet is forwarded for transmission to the destinationdevice. If the address is determined not to be recoverable, the processmoves to step 508.

In another embodiment of the present invention, the process movesdirectly from step 512 to step 520. In other words, if an address errorin an IP or MAC header is detected, the AP moves directly to determineif address information can be recovered from the data packet payload.

Because conventional 802.11 standard does not allocate specific slotsfor transmission of data between devices, it is difficult to ensure thatinterference is minimal for WiFi systems that employ multiple devices inclose proximity. However, in real-time applications such as WiFicordless phones (handsets), it is desirable to be able to operate morethan one WiFi handset of a system in close proximity where mutualinterference may be a problem. In addition, it is desirable to ensurethat data transmission is optimal in the presence of other RFinterferers. Thus, it is desirable to be able to preserve the ability toretransmit data, as provided for in the conventional 802.11 standard.However, because handsets are typically battery powered, it isundesirable for a WiFi handset to have to maintain continuous full poweroperation to monitor for incoming data packets for longer thannecessary.

FIG. 7 illustrates an exemplary frame structure 700 for enhancedreal-time WiFi communications, according to one embodiment of thepresent invention. The duration of frame structure 700 corresponds to afixed and continuously repeating interval that can be established by anAP and used to establish 802.11 links with WiFi terminals, such ashandsets. In other words, a WiFi system employing frame structure 700operates to generate a continuous series of repeating frames having theframe structure 700 in which a second frame begins at the time when afirst frame ends. For example, if the duration of frame structure 700corresponds to 10 ms, during a one minute voice communication data canbe transmitted over a series of 6000 consecutive data frames each havingthe structure of frame structure 700. In one embodiment of the presentinvention, frame structure 700 is used to establish communication linkswith WiFi handsets for voice communications, but could also be used forreal-time video or other real-time communications. The time intervalthat defines frame structure 700 can be communicated to any WiFi handsetassociating with the AP. In one embodiment of the present invention, asillustrated in FIG. 7, the time interval is 10 ms, but can be 20 ms oranother convenient duration. By establishing a fixed duration for framestructure 700, an AP can facilitate simultaneous communications withmore than one WiFi handset, as described further below.

Frame structure 700 includes handset active slot 702. The term “handsetactive slot” or “active slot” corresponds to a time interval duringwhich a designated WiFi handset that is associated with the AP canmaintain an “active” state where full power of the handset can beemployed. During the active state, the handset can, for example, receivedata, send data, and actively listen for data. In one embodiment of thepresent invention, after a handset associates with an AP employing framestructure 700, the AP can establish communications with the handsetusing frame structure 700 and an active slot can be assigned to thehandset as described below.

Referring to FIG. 8, which depicts a WiFi system 800 arranged inaccordance with one embodiment of the present invention, WiFi handset802 can power on and associate with AP 803, which is connected to IPnetwork 811. Upon power on and registration of handset 802, AP 803 canestablish a conventional 802.11 communications mode, with handset 802.In the conventional communications mode a periodic beacon is sent, forexample, every 600 ms, to indicate whether any buffered data is to besent between AP 803 and WiFi handset 802. During conventionalcommunications mode, the WiFi handset can send and receive data based onapplications that do not have a substantial requirement for real-timecommunications.

In one embodiment of the present invention, when, after registrationwith an AP, a WiFi terminal, such as handset 802, requests initiation ofa real-time 802.11 communications mode (or “real-time communicationsmode”), the AP activates a real-time communications mode by establishinga real-time communications frame structure with the requesting handset.Thus, AP 803 can respond to a request from handset 802 and forward theinformation necessary to use frame structure 700 for real-timecommunications. The request for real-time communications mode can beinitiated by a WiFi device user employing a user interface such as abutton or keypad on the WiFi device. The button could be a “phone”button that when depressed indicates that the device is going “off-hook”to participate in a telephone call. Alternatively, a button to receivestreaming audio, MPEG, etc. from an AP could also be used to initiate areal-time communications mode. Referring again to FIG. 8, uponinitiation of a real-time communications mode, AP 803 then assignsactive slot 702 to handset 802. When real-time communications mode isinitiated, during each frame 700, handset 802 is active substantiallyonly within frame 702. During “sleep period” 704, for example, a handsetthat is active in active slot 702 remains at low or standby power. Inone embodiment of the present invention, the arrangement of active slot702 and sleep period 704 is based on an Unscheduled Automatic Power SaveDelivery (U-APSD) protocol. For example, when a handset such as handset802 registers with AP 803, it can indicate that is wishes to enableU-APSD.

FIG. 9 illustrates one implementation of U-APSD. In active slots 902, agiven handset can operate at full power. During uplink transmission slot904, the handset can send data and during downlink transmission slot 906the handset can receive data from an AP. At time E, a sleep triggertime, the handset receives an end of service period (EOSP) bit thattriggers the handset to initiate a reduced power mode (“go to sleep”),which persists throughout standby slot 908 until time W, at which pointthe handset resumes active operation.

Thus, in one embodiment of the present invention, the general U-APSDmethod illustrated in FIG. 9 is applied to frame 700 to produce activeslot 702 and sleep period 704. For example, if handset 802 is assignedto slot 702, interval 902 corresponds to active slot 702 and standbypower interval 908 corresponds to sleep period 704. At time T0 of everyframe 700, handset 802 wakes up. The wakeup time T0 can be established,for example, when handset 802 initiates a request for real-timecommunications with AP 803. The AP can set the duration of frame 700 andinstruct handset 802 to wake up at time T0 of each frame. Handset 802can store this information, and based on an internal clock, handset 802can subsequently wake itself up every 10 ms, for example. In oneembodiment of the present invention, the termination of active slot 702at time TE occurs when a handset, e.g., handset 802, receives an EOSPbit from AP 803. Accordingly, handset 802 is inactive during each framefor a period corresponding to interval 704.

In a preferred embodiment of the present invention, the duration ofactive slot 702 can extend from time T0 to T1, which represents amaximum duration of an active period for a handset assigned to slot 702.For example during initiation of a real-time communications mode ofhandset 802 with AP 803, AP 803 assigns a start of a wake up period attime T0 of each frame and sets a default “go to sleep” time at T1. Ifhandset 802 has not received an ESOP bit (or other trigger to end theactive state) from AP 803 by time T1, the handset nevertheless initiatesa power down to inactive state. For example, the handset could senddummy data to a CODEC to simulate receipt of an ESOP bit followed bypowering down of the device. If an ESOP bit is received before T1, forexample, at TE or T2, then the inactive state begins for handset 802 attime T2, and continues during interval 704. Thus, interval 704 can varyfor handset 802 in each frame.

In an enhanced mode of communications between and AP and WiFi handsetsaccording to a preferred embodiment of the present invention, theduration of active slot 702 is arranged to allow a maximum amount ofretransmissions (or “retries”) of voice or other data, consistent withthe amount of handsets actively communicating with the AP, the datatransmission rate, and the need to transmit some control data. In otherwords, the duration of an active slot 702 is arranged to provide amaximum amount of retries for a handset associated with active slot 702and to establish communications between an access point and any otheractive WiFi handsets without overlap in time between active slot 702 andany other slots arranged for communication with the other activehandsets.

As in known, the 802.11 standard employs mechanisms for retries whenneeded. For example, frame structure 700 as depicted in FIG. 7corresponds to a slot structure in which communications slots arearranged for a single handset in communication with an AP. In oneembodiment of the present invention, frame structure 700 corresponds toa frame interval of 10 ms and the maximum duration of active slot 702corresponds to an interval of about 6400 μs. Within active slot 702,based on a data transmission rate of 11 Mbps, 5 retries of audio datatransmission can be performed, allowing for time for acknowledgementfrom the AP and wait time to receive an acknowledgement. Thus, ifneeded, a handset is allotted up to five retries within active slot 702to transmit data to an AP. Upon successful transmission of a datapacket, the handset can receive acknowledgment from the base AP and anESOP bit if no further data is to be transmitted from the base unit.Thus, for example, at 11 Mbps, the duration in which a handset is awakewithin active slot 702 can vary from about 700 μs up to about 6400 μs,depending on the amount of retries needed to transmit a data packet.

Frame 700 further includes command slot 708 that is used to send acommand packet between an AP and WiFi handset.

FIG. 7A illustrates frame structure 720, in accordance with anotherembodiment of the present invention. Frame structure 720 illustrates anarrangement having two handset active slots 722, 724 and command slot726. In this arrangement, each active slot can be assigned to a separateWiFi handset to establish a regular active interval to communicate witha common AP. Thus, referring again to FIG. 8, handset 802 can registerwith AP 803, initiate a request for real-time communications, and beassigned active slot 722. Handset 804 can then register, requestreal-time communications mode, and be assigned handset active slot 724.Slots 722 and 724 are arranged so that they do not overlap in time.Accordingly, real-time communications between two WiFi handsets and abase unit can be maintained using the frame structure of FIG. 7A. Forexample, users of two WiFi handsets could maintain a voice call with athird party as well as hear each other.

In other words, voice data that is transmitted to and from each WiFihandset could be buffered and transmitted at 10 ms intervals, forexample, within their respective active slots, without mutualinterference.

Preferably, the operation of handset active slots 722, 724 is inaccordance with the principles described for handset active slot 702 offrame structure 700. Thus, in actual operation each slot 722, 724 canvary in duration up to a maximum active time set as default within anygive frame.

In one embodiment of the present invention, the duration D of frame 720is about 10 ms, and the duration of handset active slots 722 and 724 areequal. As depicted in FIG. 7A, time T5 corresponds to the start ofhandset active slot 724. In a preferred embodiment of the presentinvention, the time interval TN between the onset of active slots 722and 724 is arranged to fulfill two criteria: In the first case, TN ismade sufficiently long to accommodate a handset active slot 722 that canaccommodate a maximum amount of data retries at a given datatransmission rate for a first handset;

secondly, the time T5 that marks the onset of a handset active periodfor a second handset is set for maximum adaptability to changedtransmission conditions. In particular, T5 is set such that it does notneed to be changed within frame 720 when the data transmission ratebetween handsets and AP is changed and/or when the additional handsetsbecome active.

In a preferred embodiment of the present invention, time T5 is setwithin frame 720 such that the data transmission rate can be changedfrom 11 Mpbs to 5.5 Mbps to 2 Mbps, and the amount active of handsetsincreased up to six without changing the relative interval between T5and T0.

By providing a fixed time for T5, the present invention operates tominimize the amount of disruption caused by the need to adjust theposition of handset active time slots when conditions change. In oneexample where the duration of frame 720 is 10 ms, interval TN is about3900 μs. Within an interval of 3900 μs, handset active slot 722 (as wellas 724) having a duration of about 3100 μs, can be accommodated. Thisprovides for two retries for a standard 640 bit voice packet transmittedat 11 Mpbs. In addition, the duration of handset active slot 722 (aswell as 724) can be increased up to about 3700 μs, and still beaccommodated within TI, which provides for two retries for a standard640 bit voice packet transmitted at a 5.5 Mpbs. This is particularlyadvantageous when the transmission environment becomes noisier andcreates more errors in transmission between a handset and base (AP),such that a lower transmission rate is desirable. Thus, referring againto FIG. 8, with the use of frame structure 720, transmissions betweenWiFi handsets 802, 804 and AP 803, can be changed from a rate of 11 Mbpsto 5.5 Mpbs without any changes in the fixed points of the framestructure, T0 and T5. End times T4 and T6 of handset active slots 722and 724, respectively, can be governed by the receipt of a ESOP bit asdiscussed above, in which case no extra information is needed from theAP. Additionally, as noted above, the default time setting for when anactive handset would be put to sleep even if no ESOP bit is received,would be set at times TM1 and TM2. In this case, for 11 Mbps datatransmission rate, default “go to sleep” times for TM1, TM2, could beset, for example, at 3100 μs after respective wake up times T0 and T5.At 5.5 Mbps data transmission rate, default “go to sleep” times for TM1,TM2, could be set, at 3700 μs after respective wake up times T0 and T5.In either case, no rearrangement of the slots within frame structure 720is needed.

FIG. 7B illustrates an exemplary frame structure 740 arranged inaccordance with another embodiment of the present invention. Framestructure 740 is used to illustrate handset active time slot allocationin the case where four WiFi handsets are actively communicating with anAP. Frame structure 740 includes exemplary handset active slots 722 and724 of FIG. 7A. In this case, slot 722 maintains the same time intervalas in the scenario depicted in FIG. 7A where only two WiFi handsets areallocated active slots. Thus, using FIG. 8 for illustration, if handset802 is first to register with AP 803 and is assigned slot 722, in thescenario depicted in FIG. 7B, handset 802 is allocated active time thatcan accommodate 2 retries of data transmission at either 5.5 or 11 Mpbsfor a 10 ms total duration of frame 720. Comparison of FIG. 7A to 7Billustrates that wake up times T0 and therefore T5 remain the same whenthe amount of active WiFi handsets increases from two to four. Thus, ifhandsets 802 and 804 represent the first and second registered handsetswith AP 803, the wakeup times remain the same when new handsets 808, 810are associated with AP 803. However, in this case the slot width ofhandset active slots 724 for handset 804, as well as that of slots 742and 744 for handsets 808 and 810, are only sufficient for one attempt atdata transmission with no retries. Thus, in this case, in order toaccommodate communication with two extra WiFi handsets, only one timingchange needs to be sent to the previously associated handsets, namely anew default go to sleep time TM2.

FIG. 7C illustrates a frame structure 760 that adds two handset activeslots 762, 764 to the arrangements of slots depicted in FIG. 7B. The twonew slots correspond to slots allocated to a fifth and sixth WiFihandset to associate with an AP. In this case, slot 722 for handset 802is also adjusted such that only a single data transmission can beaccommodated without any retries. As noted above, however, T5 ispreferably arranged such that handset active slots for six activehandsets can be accommodated for data transmission rates of both about11 and 5.5 Mbps, without a change in the time interval TN.

FIG. 7D illustrates a frame structure 770 that corresponds to a scenarioin which an extra handset active slot 762 is added to two previouslyactive handset slots 722, 724 in the case where the data transmissionrate is also drastically reduced. For example, the relative arrangementof slots within frame structure 770 as compared to 720 can illustratethe case in which the data transmission rate is reduced from 11 to 2Mbps, and a third handset active slot is added. Once again, the positionof T0 and T5 is not altered, so that, referring back to FIG. 8, thewakeup times for WiFi handsets 802, 804 is not changed. In this case, goto sleep time TM1 is sufficient to accord the first registered handset802 time for one retry of data transmission. In addition, slots 724 and742 for handsets 804 and third handset 806, respectively, onlyaccommodate one data transmission and no retries.

In accordance with another embodiment of the present invention, handsetactive slots can be dynamically reassigned when an active WiFi deviceceases real-time communications. Thus, referring to FIGS. 7D and 7A, theframe structure of FIG. 7D could be reconfigured when “HS2” ceasesreal-time communications. For example slots 722, 724, and 742 can beused to provide simultaneous voice communications for three handsetsduring a phone call routed through a common AP. If, during the phonecall, HS2 goes on-hook, a signal is sent to the AP that indicates thatslot 724 is available. Accordingly, slot 724 can be reassigned by the APto HS3 which is in communications with the AP through slot 742. Inaddition, because the AP knows that only two handsets are now inreal-time communications mode, it can reconfigure slot 724 and expandthe maximum duration of the slot as defined by TM2, such that TM2 ismoved to a point such as represented in FIG. 7A. Accordingly, the amountof retries for HS3 can be increased. If any additional handsetssubsequently go off-hook to join the conversation, the active slotassignment can proceed as indicated in the progression of FIGS. 7B and7C, with the “old” HS3 now assigned to slot 724.

In another embodiment of the present invention, dynamic reassignment ofWiFi devices are employed to reassign WiFi devices when the firstpriority slot, e.g., slot 722 becomes unoccupied. Thus, in the scenarioof FIG. 7D, when HS 1 goes on hook during a common phone call, HS2 canbe reassigned to active slot 722 and HS3 reassigned to an expandedactive slot 724, as represented by FIG. 7A.

FIG. 7E illustrates a frame structure 780 that adds a fourth handsetactive slot 782 in the case of a lower data transmission rate, asillustrated in FIG. 7D. In this case, slot 722 for handset 802 is alsoadjusted such that only a single data transmission can be accommodatedwithout any retries. As noted above, however, T0 and T5 remainunchanged.

It is to be noted that, although in reality a single sleep period for aWiFi device comprises an uninterrupted interval, for a single frameinterval of the frame structure depicted in FIGS. 7A-7E, only the sleepperiod for a device corresponding to active slot 722 extendscontinuously (from T6 or T0 of the subsequent frame) for the respectiveframe depicted. For example, for a device corresponding to active slot724, a complete sleep period comprises a portion of a sleep periodextending between T0 and T5 that occurs before wake-up at T5, and aportion of the sleep period that occurs between T6 and T0 of asubsequent frame.

FIG. 10 illustrates exemplary steps in a method for enhancedcommunications in a WiFi system, according to another embodiment of thepresent invention. In step 1002, a registration is received from a WiFidevice (handset), for example, when the WiFi device powers on. When theregistration from the WiFi handset is received at a base unit of a WiFisystem (AP), the WiFi handset indicates to the base unit that in areal-time communications mode, it wishes to enable a mechanism toallocate an active period and sleep period for the WiFi handset withineach frame. For example, the WiFi handset indicates that it wishes toenable an Unscheduled Automatic Power Save Delivery (U-APSD) mechanismto control active and sleep periods. The base unit then configurescommunication to be both trigger and delivery enabled during real-timecommunications.

In step 1003, if a request for real-time communication is not received,the process moves to step 1004.

In step 1004, the WiFi device proceeds in a conventional communicationsmode used for non-real-time applications. For example, afterregistering, the WiFi device may continue to receive data through aconventional 802.11 data link from the AP that it is registered with.

If, in step 1003, a real-time communications request is received fromthe registered WiFi device, a real-time 802.11 communications mode isinitiated, as embodied in steps 1005 and 1006. In step 1005, a real-timeframe (or communication frame) is established.

The real-time frame is established by the AP to facilitate exchange datafor applications such as voice or streaming audio. The real-time frameis characterized by a frame interval, which corresponds to the timebetween sending of successive data packets as described above withrespect to FIG. 7. For example, in a WiFi system in which WiFi handsetsare used as cordless telephones, the frame interval corresponds to thetime between sending of successive audio packets. In an exemplaryembodiment of the present invention, this frame interval is 10 ms.

In step 1006, a regular wake-up time is reserved for the first WiFihandset. Preferably, the wake-up time corresponds to a fixed pointwithin each communications frame at which the first WiFi handset is towake-up. For example, an AP receiving a telephone call set-up for thefirst WiFi handset reserves a wake-up time at the time of call set-up.After receiving the wake-up time, the first WiFi handset can set aninternal clock to wake itself up at the wake-up time within eachsubsequent frame. In addition, a default sleep time is set relative tothe wake-up time which signifies the point at which the first WiFihandset is to enter low power or standby power operation. The wake-uptime and default sleep time serve to define a default active slot, whichdefines a maximum period for full power operation of the WiFi handsetwithin a communications frame. Thus, during operation, if the first WiFihandset receives no ESOP bit indicating the onset of sleep mode, at atime defined by the default sleep time, the first WiFi handsetnevertheless enters low power or standby power mode during each frame.The default active slot thus corresponds to a time interval within eachframe interval that is available for the first WiFi handset to operateat full power to enable transmitting and receiving data. In a preferredembodiment of the present invention, the actual duration of the activeslot can vary based on the U-APSD protocol discussed above, but does notexceed the duration of the default wake-up slot. In other words, a sleeptrigger time can be established within each communications frame inwhich an ESOP bit is scheduled to be delivered. The sleep trigger timecan thus be set to occur any time before the default sleep time. Thus,within every communication frame, the first WiFi handset operates atfull power during the active slot and at reduced power during theremainder of the frame interval.

Preferably, the default active slot is arranged so as not to overlap intime with any other wake-up slots that may be arranged with additionalWiFi devices linked to the AP.

In step 1007, if an additional WiFi request for real-time mode isreceived, the method moves to step 1104 of FIG. 11, described in detailbelow.

If no additional request for real-time mode is received the processmoves to step 1008. In step 1008, when a wakeup time arrives for a WiFidevice, the method moves to step 1010. For example, the wake-up timecould correspond to that of the first WiFi device.

In step 1010, the WiFi device is awakened. For example, the WiFi devicecould be a handset that is awakened based on an internal clock in thehandset. At the time of registration (association) with the AP, thehandset and AP exchange information that sets the communications frameand the wake-up time within each frame for the WiFi handset.Accordingly, the WiFi handset knows that it is to wake up periodicallyat the pre-defined wake-up times that can be stored and initiated whenthe internal clock indicates that the wake-up time has arrived.

In step 1012 a data delivery trigger is received. The trigger could be,for example, a voice packet received from the WiFi device.

In step 1014, buffered data is delivered to the WiFi device over theWiFi link between the device and AP. The delivery takes place during theactive slot. Within the active slot the device can send and receive datafrom the AP. Depending on other parameters discussed above, data packetsmay be sent in retries multiple times within an active slot.

In step 1016, if an ESOP bit is received, the method moves to step 1018.For example, after receiving and sending information, the AP mayindicate to the WiFi device that it has successfully received data sentfrom the handset and that no further data is to be sent.

In step 1018, the WiFi device is put to into a standby or reduced powermode.

If an ESOP bit is not received, the method moves to step 1020. In step1020, if the default sleep time has been reached, the method moves tostep 1018. If the default sleep time has not been reached, the methodreturns to step 1016.

In step 1022, if real time communication has been terminated between theWiFi device and AP, for example, if the WiFi device goes on hook after atelephone call, the method moves to step 1023. If the real timecommunication with the WiFi device is not terminated, the processreturns to step 1008 where the arrival of a subsequent wake-up timetriggers another process of waking up of a WiFi device.

In step 1023, if the WiFi device has powered down, the process moves tostep 1024.

If the WiFi device is still powered on, the process moves to step 1004where the WiFi device proceeds in a conventional 802.11 communicationsmode.

In step 1024, if real-time communications are terminated with all WiFidevices registered to an AP, the process moves to step 1025. Ifreal-time communications mode persists with at least one other WiFidevice, the process moves to step 1008 and cycles through steps1008-1022 for each device still in real-time communications mode.

In step 1025, if not all WiFi devices are powered off, the processreturns to step 1004 for devices still powered on. Subsequently, thedevices can re-initiate a request for real-time communications, forexample, by going off-hook to participate in a telephone call. If alldevices are powered off, the process ends.

Preferably, the above method can be employed between multiple WiFidevices that are in communication with a common AP at the same time. Theuse of the term “same time” (or simultaneously), unless otherwiseindicated, is meant to indicate that multiple WiFi devices can interactwith an AP over the same long term time interval, for example measuredin seconds or minutes, even if actual communications within a 10 msframe are arranged in mutually exclusive time slots. Thus, the method ofFIG. 10 can be employed simultaneously with many WiFi handsets, as longas active slot space is available, as illustrated above, in FIGS. 7A-7E.

FIG. 11 illustrates exemplary steps in a method for enhancedcommunications in a WiFi system, according to another embodiment of thepresent invention.

In step 1 102, a first default active slot is reserved for a first WiFidevice. For example, as described above with respective to FIG. 10, theactive slot could be reserved when real-time communications mode isinitiated for the first WiFi device.

In step 1104, a second default active slot is reserved for a second WiFidevice, for example, after initiation of a real-time communications modewith the second WiFi device. Preferably, the first and second defaultactive slots do not overlap in time.

Accordingly, the first and second WiFi devices can actively communicatewith an AP without interfering with one another. Preferably, theduration of the first and second active device slots are such that amaximum of retries can be performed during the time a respective WiFidevice is active. Thus, the spacing of wake-up times between the firstand second default active slot is arranged so that the first defaultactive slot provides a maximum amount of retries for the first WiFidevice. In an exemplary embodiment of the present invention, both firstand second active device slots accommodate two retries within a frameinterval of about 10 ms using data transmission rates of about 5-12Mbps.

In step 1106, if no additional device requests real-time communicationsmode initiation, the process moves to step 1008. If an additionalrequest for real-time communications mode is received, the process movesto step 1108.

In step 1108, the default sleep time is adjusted on the second activeslot. For example, referring to FIGS. 7A and 7B, the default sleep timeTM2 for slot 724 is adjusted to an earlier time to accommodate theaddition of handset 3. After adjustment of the default sleep time, theamount of retries available for data transmission for the second WiFidevice within slot 724 is reduced. However, the amount of retriesavailable for the first WiFi device remains unchanged.

In step 1110, a third default active slot is reserved for a third WiFidevice, as illustrated, for example, in FIG. 7B for handset 3. In thiscase, the amount of retries available to a third device registering in athird active slot is no greater than that of the second WiFi device. Forexample, the third active default slot can be arranged so that it beginsat a time that occurs before the unadjusted default sleep time of thesecond active slot (see TM2 of FIG. 7A), but after the adjusted defaultsleep time of the second active slot (see TM2 of FIG. 7B).

In step 1112, if no additional device requests real-time communicationsmode are received, the process moves to step 1008. If an additionalreal-time communications mode request is received, the process moves tostep 1114.

In step 1114, a fourth default active slot is reserved for a fourth WiFidevice, as illustrated, for example, in FIG. 7B for handset 4. In thiscase, the amount of retries available to a fourth device registering ina fourth active slot is no greater than that of the second WiFi device.

In step 1116, if no additional device requests real-time communicationsmode, the process moves to step 1008. If an additional real-timecommunications mode request is received, the process moves to step 1118.

n step 1118, the default sleep time is adjusted on the first activeslot. For example, referring to FIGS. 7B and 7C, the default sleep timeTM1 for slot 722 is adjusted to an earlier time to accommodate theaddition of handset 5. After adjustment of the default sleep time, theamount of retries available for data transmission for the first WiFidevice is reduced, as illustrated in FIG. 7C.

In step 1120, a fifth default active slot is reserved for a fifth WiFidevice, as illustrated, for example, in FIG. 7C for handset 5. In thiscase, the amount of retries available to a fifth device registering in afifth active slot is no greater than that of the other WiFi devices.

In other embodiments of the present invention, the method illustrated inFIG. 11 can be extended to accommodate additional WiFi devices, assuggested by FIG. 7C where six handset slots are available to establishcommunication with six devices simultaneously.

In accordance with the method of FIGS. 10 and 11, a first WiFi device torequest real-time mode initiation (requesting device) is accordedpriority in terms of the amount of redundancy (retries) accordedcommunications between the WiFi device and AP. This provides forenhanced quality of real-time communications for the first requestingdevice while still permitting other devices to link with the AP in thereal-time communications mode. Thus, for example, when more than oneWiFi handset desire to link to a single active call, an AP can mix theaudio data to and from handsets so that the WiFi handset users canlisten and talk to each other.

The method also provides a mechanism to ensure that a plurality of WiFidevices can receive and send data on a “real-time” basis, for example,every 10 ms, without having to spend unnecessary time in a full powerstate listening for incoming data. In addition, because all registeredWiFi devices within a communications range of an AP have their activecommunications scheduled in separate time slots, a registered WiFidevice employing 802.11 communications protocol potentially spends lesstime “backing off” from radio traffic that might otherwise be presentduring the active period of the registered WiFi device.

Additionally, as discussed above in reference to FIGS. 7-7E, managementof communications is simplified by requiring a minimum of changes inactive slot configuration when the amount of active WiFi devices isaltered.

In summary, in one embodiment of the present invention method forenhanced payload protection in a WiFi system includes the steps of: a)receiving a first data packet in a buffer; b) transmitting the firstdata packet and a second data packet in a first frame body, the datapackets transmitted between a WiFi terminal and access point (AP); c)transmitting the first data packet and a third data packet in a secondframe body, the data packets transmitted between the WiFi terminal andaccess point (AP); d) repeating the steps a) through c) wherein twocopies of each data packet are transmitted in subsequent frame bodies;and e) forwarding a best copy of the two copies of each data packet to areceiver.

In another embodiment of the present invention, a method for enhancedpayload protection in a WiFi system includes the steps of: a) Storing adata packet in a buffer; b) Storing an FEC packet based on the datapacket in the buffer; c) transmitting the data packet and FEC packetbetween a WiFi terminal and access point; d) applying the FEC packet tothe data packet to produce a corrected data packet; and e) forwardingthe corrected data packet to a receiver.

In a further embodiment of the present invention, a method for enhancingcommunications over a WiFi link includes the steps of: a) transmitting adata payload over a first payload; b) detecting an error using an FCSpacket; c) sending the data payload to a packet correction layer; d)determining the nature of the error; e) determining that an IP addresserror has occurred; and f) recovering a destination for the data payloadbased on a unit ID packet.

In still another embodiment of the present invention, a method forenhanced communications in a WiFi network includes the steps of a)receiving registration from a WiFi device; b) establishing a real-timecommunications mode with the WiFi device that includes the steps of andaccess point (AP); c) establishing a communications frame with the WiFidevice and; d) arranging within the frame an active timeslot fortransmission of audio data packets between the WiFi device and AP; e)receiving a trigger from the WiFi device; and f) delivering bufferedaudio data to the WiFi device, wherein the active timeslot is configuredto avoid overlap with active timeslots of other registered WiFi devices.

The foregoing disclosure of the preferred embodiments of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many variations andmodifications of the embodiments described herein will be apparent toone of ordinary skill in the art in light of the above disclosure. Thescope of the invention is to be defined only by the claims appendedhereto, and by their equivalents.

Further, in describing representative embodiments of the presentinvention, the specification may have presented the method and/orprocess of the present invention as a particular sequence of steps.However, to the extent that the method or process does not rely on theparticular order of steps set forth herein, the method or process shouldnot be limited to the particular sequence of steps described. As one ofordinary skill in the art would appreciate, other sequences of steps maybe possible. Therefore, the particular order of the steps set forth inthe specification should not be construed as limitations on the claims.In addition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and still remain within thespirit and scope of the present invention.

1. A communications system configured to transmit over an RF link usingan 802.11 protocol, the communications system having a data payloadstructure comprising: a first voice packet slot configured to receive afirst voice packet at a first time; a second voice packet slotconfigured to receive a second voice packet different from the firstvoice packet at the first time; and a frame check sequence packet,wherein the first voice packet slot is configured to receive the secondvoice packet at a second time subsequent to the first time.
 2. Thecommunication system of claim 1, further comprising a third voice packetslot configured to receive a third voice packet at the first time,wherein the second voice packet slot is configured to receive the thirdvoice packet at the second time.
 3. A communication system configured totransmit over an RF-link using an 802.11 protocol in which a data packetstructure comprises: a data packet transmitted as part of an 802.11payload packet; and a forward error correction packet having forwarderror correction bits calculated from the data packet by a transmitterof the communications system.
 4. A method of transmitting an IP packetusing an 802.11 link, comprising: receiving the IP packet over an airinterface, the IP Packet containing a data packet payload; detecting anerror in the IP packet; forwarding the IP packet to a packet evaluationlayer; and correcting the error and forwarding the IP packet fordelivery if the error is not an address error.
 5. The method of claim 4,further comprising; determining that the error is an address error; andcorrecting the error and forwarding the IP packet for delivery if theaddress error is determined to be recoverable from an IP or MAC header.6. The method of claim 4, further comprising; determining that the erroris an address error; determining that the address is not recoverablefrom an IP or MAC header; determining that the address is recoverablefrom a data packet in the IP packet; and correcting the address errorand forwarding the IP packet for delivery.
 7. The method of claim 4,wherein the IP packet comprises VOIP data.
 8. The method of claim 4,further comprising; determining if the IP packet was received from adevice registered with the communications system; and rejecting the IPpacket if the IP packet was received from an unregistered device.
 9. Themethod of claim 6, wherein the data packet comprises: a voice payload tocarry voice data; a unit ID packet obtaining information uniquelyidentifying a destination device for the IP packet; and an FEC packetconfigured to correct errors in the Unit ID packet.
 10. A WiFicommunication system having a frame structure for transmitting datapayloads between an access point and one or more WiFi terminal devices,the frame structure comprising: a frame period that is a fixed andrepeating time interval during which a WiFi link is operable between theaccess point and WiFi terminal devices; one or more of the active slots,each active slot dedicated to a respective WiF terminal device, wherethe respective WiFi terminal device maintains an active state onlyduring the respective active slots; a sleep period associated with eachWiFi terminal device, wherein the respective WiFi a terminal devicemaintains a low or standby power state in the sleep period; and acommand slot configured for transmission of a command packet between theaccess point and the WiF terminal device.
 11. The WiFi communicationssystem of claim 10, wherein the sleep period is configured to start whenthe WiFi terminal device receives an EOSP bit from the access point. 12.The WiFi communication system of claim 10, wherein the sleep period isconfigured to start at a default sleep time if an EOSP bit is notreceived.
 13. The WiFi communication system of claim 10, wherein a firstactive slot of the one or more active slots is confirmed to allow amaximum amount of retries of data transmission between a first WiFiterminal device and an access point, wherein the first active slot doesnot overlap in time with any other slots arranged for communication withother active WiFi devices.
 14. The WiFi communication system of claim13, wherein the frame structure comprises: a first wakeup time thatmarks a start of a first active slot corresponding to an active periodof a first WiFi terminal device; and a second wakeup time that marks astart of a second active slot corresponding to an active period of asecond WiFi terminal device, wherein the first and second active slotsdo not overlap in time.
 15. The WiFi communication system of claim 14,wherein the first wakeup time and second wakeup time are mutuallyarranged such that additional active time slots for additional WiFidevices can be incorporated in the frame structure without adjusting thesecond wakeup time.
 16. The WiFi communication system of claim 14,wherein the first wakeup time and second wakeup time are mutuallyarranged such that a transmission rate between active WiFi terminaldevices and the access point can changed be changed without adjustingthe second wakeup time.
 17. A method for real-time communications in aWiFi communications system comprising: receiving a real-timecommunications request from a first WiFi device that is registered withthe system; establishing a real time communications date frame structurecorresponding to a plurality of repeating data frames duringcommunications between the first WiFi device and an access point;reserving a first default active slot comprising a first wakeup time andfirst default sleep time within each repeating data frame; initiating anactive period of the first WiFi device during each repeating data frameat the wakeup time; and terminating the active period of an ESOP bit isreceived.
 18. The method of claim 17, further comprising: establishing asleep trigger time at witch the system is configured to deliver the ESOPbit to the first WiFi device; and terminating the active period at adefault sleep time if the ESOP bit is not received before the defaultsleep time.
 19. The method of claim 17, further comprising: receiving atrigger; and delivering buffered data to the WiFi device during theactive period.
 20. The method of claim 17, further comprising: receivinga second real time communication request from a second WiFi device; andreserving a second default active slot for a second WiFi device, whereinthe first and second default active slots do not overlap in time,wherein the second default active slot comprises a second wakeup timeand second default sleep time.
 21. The method of claim 20, furthercomprising: receiving a third request for real-time communications froma third WiFi device: adjusting the second default sleep time; andreserving a third default active slot for the third WiFi devicecorresponding to a third wakeup time and a third default sleep time,wherein the adjusted second default sleep time is before the thirdwakeup time, and wherein the unadjusted second default sleep time isafter the third wakeup time.